Preparation And Structure Optimization Of Alumina Ceramic Membrane Based On Transfer Film Method

Compared with polymer membranes,ceramic membranes have outstanding application prospects because of their excellent mechanical properties,stability,easy cleaning and longer membrane life.However,ceramic membrane filtration technology still has many challenges in industrial applications,which need to be resolved in future research.The main reason that restricts the wide application of ceramic membranes is the ultra-high cost of ceramic membranes,which is caused by expensive raw materials and complicated preparation processes.Many researchers employed cheap raw materials to prepare ceramic membranes at a lower cost.However,under the premise of ensuring excellent mechanical and chemical properties,the research on optimizing performance and reducing complex processes from a process perspective is slightly insufficient.Especially on the basis of traditional methods of preparing ceramic membranes,such as dip-coating and spray-coating,it is difficult to further enhance and improve the performance of ceramic membranes,and to obtain products with higher commercial value.For most ceramic membranes with asymmetric structures,the optimal design of the structure is very important,but there is currently a lack of systematic guidance.Starting from the performance matching of the ceramic membrane support and the intermediate layers and membrane layers,optimizing the performance of the ceramic membrane is often overlooked.Traditional ceramic membranes are generally designed as a multi-layer gradient pore structure.This structure gradually transitions from the macroporous support at the bottom to the middle layer,and then to the separation layer on the top layer,with the pore size gradually decreasing.The balance between the permeability and selectivity of the membrane is the main consideration in the design of ceramic membranes,that is,in practice,ceramic membranes usually have to reduce membrane flux to obtain high rejection rates.But in fact,there are structures that impair performance such as unnecessary intermediate layers or particle penetration layers in the ceramic membrane,once they can be removed or their effects can be reduced,the rationality of the structure will be greatly improved.In order to improve the mechanical properties of the support while obtaining excellent permeability,Zr O_2(f)is used to toughen it.After the characterization of porosity,pore size and mechanical properties,it was found that by introducing Zr O_2(f),the mechanical strength and permeability of the Al₂O₃ support were sufficiently improved.The straight morphology and smooth surface of Zr O_2(f)reduce the flow resistance and increase the connectivity of the pores.In addition,clear evidence of fiber-reinforced mechanism is observed on the fracture surface,which indicates that Zr O_2(f)has advantages in improving support strength.The support sintered at 1550?is regarded as the optimized sample,with a pore diameter of 3.25?m,a bending strength of 82.3±10.2 MPa,and a pure water flux of 25.9 m³m^-2h^-1bar^-1.On the basis of previous research,we have developed a transfer film method for ceramic membrane preparation.Different from traditional methods,we first prepare a flexible pre-membrane by tape-casting,and then attach it to the wetted support.During the drying and sintering process,the pre-membrane will form a ceramic filtration membrane layer and be tightly combined with the support to obtain the final ceramic membrane product.In this method,the dependence of the molding process on the support is much less than other traditional preparation methods,so the membrane layer also has good adaptability to different supports.Because the membrane formation process is uniform and slow,the phenomenon of particle penetration is fundamentally avoided,and the prepared membrane layer exhibits extremely narrow pore size distribution and high flux.By adjusting the slurry solid content,organic content and membrane thickness,sintering temperature and other parameters in the formula,the pore size and permeation flux of the membrane have been precisely controlled.In view of the problem of membrane particles infiltrating into the support in the traditional ceramic membrane preparation method,as well as the high preparation cost caused by raw materials and multiple high-temperature treatments,the transfer film method was together used with co-sintering technology for manufacturing low-cost and high-performance ceramic membranes was first proposed.With the assistance of Si O₂ sol,the Al₂O₃ support has achieved a bending strength of 23.5 MPa and an ultra-large permeation flux of up to 198 m³m^-2h^-1bar^-1,which provides a basis for the preparation of high flux membrane systems.The high binder content in the pre-membrane avoids cracks and produces high porosity,thereby giving the film a high selectivity.After only one sintering process,the average pore size of the microfiltration layer prepared at 1300?is 249 nm,and it shows a very narrow pore size distribution,with the maximum pore size being only 287 nm.The membrane also has a high-purity water flux of5040 Lm^-2h^-1bar^-1 and a rejection rate of 96.2%for carbon ink with an average particle size of237 nm.The transfer film method prepares membranes with the same properties on supports with different fluxes,and their thickness and pore size distribution are consistent.On this basis,the influence of the flux of the support on the system flux was studied.The results showed that with the increase of the flux of the support,the flux of the membrane system first increased rapidly,then slowly increased and stabilized.Combining this rule,Darcy's theorem was used here to derive the possible system limit flux(J_lim).Considering the influence of the flux of the support on the system flux,we propose a scientific design method that can match the flux and mechanical properties of the support with the given requirements to the membrane layer,and use the ratio of the membrane resistance to the total filtration resistance(b)as a criterion,and provides evaluation and suggestions on the matching of support and membrane for the existing ceramic membrane system.The ceramic membranes with similar properties were prepared by the transfer film method and the immersion pulling method,and the difference in permeability was compared,and the filtration resistance of the permeable layer and the intermediate layer was measured,which provided a new idea for optimizing the structure of the ceramic membrane.